Manufacture of viscose



Patented Dec. 6, 1938 UNITED STATES MANUFACTURE OF VISCOSE Jacob de Buoys, Breda, Netherlands, assignor to American Enka Corporation, Enka, N. 0., a corporation of Delaware No Drawing. Application October 21, 1937, Serial No. 170,292. In the Netherlands October 23,

7 Claims.

This invention relates to the manufacture of viscose artificial silk and more particularly to a novel method of controlling and regulating the viscosity of viscose spinning solutions.

During the conventional processing steps to convert cellulosic material into spinning solutions of the viscose type, the alkali cellulose must be suitably aged in order to provide a spinning solution having the proper viscosity for practical working operations. If the aging step be omitted, then the viscosity of the viscose solution is too high. It is well known that the degree of aging is dependent on several factors, e. g., aging temperature, aging time and the amount of oxygen coming in contact with the alkali cellulose. If the air containing oxygen is prevented from contacting the alkali cellulose, substantially no aging occurs, or at least, it occurs much more slowly.

A number of methods have been proposed to effect the proper viscosity of spinning solutions without the aging step. Naturally the complete elimination of the aging operation is highly desirable from the standpoint of economy of time and space required for this particular step. In fact, any shortening of the aging period has its advantages.

The aging being dependent on temperature, attempts have been made to utilize higher temperatures to accelerate this period. However, certain objections at once become apparent because either the immediately succeeding sulphurizing step must be carried out at higher temperatures for which the usual sulphurizing apparatus is not adaptable, or the alkali cellulose must be cooled before sulphurizing, thereby involving the danger of the formation of water on the walls of the container. This water when coming in contact with the alkali cellulose will form lumps, which prevents uniform sulphurizing and inhibits filtering and spinning of the viscose.

Still another proposal to reduce the viscosity contemplates the contacting of alkali cellulose with a gas that is richer in oxygen content than is the atmosphere. This method also has objections and is far from economical.

Finally, it has been suggested to add different chemicals to the caustic soda steeping solution, for example, peroxides, diand polyvalent alcohols or sodium sulphide. These chemicals, however, produce objectionable secondary reactions and moreover increase the costs of manufacture.

It is, therefore, the object of the present invention to provide a method whereby the aging of the alkali cellulose can be entirely eliminated or, at least, theaging period shortened considerably.

A further object contemplates a relatively simple process that can be practiced without the use of any special chemicals and at normal temperacifically..the normal xanthating operation is interrupted after only a portion of the usual quantity of carbon disulphide has been added. When this definite amount of carbon disulphide has been absorbed by the alkali cellulose crumbs,

then Without stopping the churn, air is blown in i,

the sulphurizing zone for a short period. Upon the completion of the air treatment the remaining quantity of carbon disulphide necessary to fully react with the alkali cellulose is added in the normal way and the resulting cellulose Xanthate is dissolved in dilute alkali to form viscose. Inexplicably, it has been determined, that the decrease in viscosity of the viscose according to this method is much greater than when the same amount of air contacts with entirely undesulphurized alkali cellulose or with normally finished xanthate, the temperature being. maintained the same in all cases.

By varying the ratio of the quantities of carbon disulphide added before and after blowing the air through the xanthating zone the decrease in viscosity of the spinning solution passes through a sharply defined maximum. The maximum decrease in viscosity is obtained when the quantity of carbon disulphide added before introducing the air is between 60. and of the total quantity needed.

By Way of example, the tables set forth below indicate the results of several experiments. These results were obtained when using an alkali cellulose without aging and having a composition comprising 15.5% sodium hydroxide and 29% cellulose and other innocuous constituents. The figures which indicate the final viscosity of the viscose are expressed in seconds and are determined by means of a tube-viscosimeter. This viscosimeter consists of a vertical glass-tube of 5.2 mm. internal diameter, open at both ends and which possesses two marks at a distance of 230 mm. The tube is filled with viscose, which is then allowed to flow out under the influence of its own hydrostatic pressure. The time in seconds it takes the viscose meniscus to flow from the upper mark to the lower one, is taken as the viscosity of the Table I Tcikiliperature at Win02 t e air reaction 00 Period of blowing place air Seconds Seconds r 125 In the above table when blowing the air through the xanthating zone for one hour and two hours, respectively, at 25 C., the viscosities were outside of the range of interest. When air was blown through for three hours at 30 C., the viscosity being 35", no further blowing was necessary and accordingly, no figure was given for the four-hour period.

In order to compare the above viscosities with the viscosity of the spinning solutions in which the air has been contacted with undesulphurized alkali cellulose and normal xanthate manufactured by the addition of 37% carbon disulphide the following table is given. In this case the reaction time was three hours.

It readily can be seen from the foregoing that with very little extra cost and no alterations in the apparatus involved, the viscosity of the viscose can be decreased materially. The viscose so obtained is in all respects of normal behavior throughout the steps followed to convert the same into rayon.

What is claimed is:

l. A preparatory treatment for the manufacture of viscose having a normal viscosity from unaged alkali cellulose which comprises forming alkali cellulose and immediately partially sulphurizing the same, suspending the sulphurizing step and introducing air into the alkaline sulphurizing zone and finally completing the sulphurizing action on the alkali cellulose to produce cellulose xanthate.

2. A method of converting unaged alkalicellulose into viscose having a normal viscosity which comprises incompletely xanthating alkali cellulose immediately after it has been formed, contacting air containing oxygen with the partially reacted alkaline mass for a limited period, completing the xanthating operation and dissolving the cellulose xanthate in a dilute caustic solution to produce viscose.

3. A method according to claim 2 which further provides for the addition of 60 to of the total amount of carbon disulphide needed prior to the introduction of air.

4. A method of converting unaged alkali cellulose into viscose having a normal viscosity which comprises partially xanthating alkali cellulose by reacting 25% carbon disulphide, based on the weight of dry cellulose in the alkali cellulose, with alkali cellulose, blowing air containing oxygen in the xanthating zone for at least two hours, completing the xanthating operation by the further addition of 12% carbon disulphide based on the weight of dry cellulose in the alkali cellulose and dissolving the thus formed cellulose xanthate in a dilute caustic solution to produce viscose.

5. A method according to claim 4 in which the air is blown in the xanthating zone for 3 to 4 hours at approximately 25 C.

6. A method according to claim 2 which further provides for contacting air with the partially reacted mass for a period from three to four hours at a temperature of approximately 25 C.

7. A method according to claim 4 in which JACOB DE BOOYS. 

